Transposition of the yeast transposon, Ty, occurs via an RNA intermediate. There is now overwhelming evidence that Ty mRNA is reverse transcribed by a Ty-encoded enzyme, probably in a cytoplasmic virus-like particle. Presumably, the rest of the transposition process occurs by a mechanism similar to that of retroviral integration, but none of the details of the process are known. Yeast is an organism which is easily manipulated genetically, allowing rapid structure/function analysis of complicated biological processes like transposition. The goal of this project is to determine the mechanism by which Ty reverse transcripts are integrated into the target DNA through a study of sites on the Ty DNA (cis elements), Ty-encoded gene products (trans elements) and additional non-Ty genes required for the transposition process. A combined genetic, molecular biological, and biochemical approach will address the following specific experimental aims: 1) To identify sequences within the Ty element required in cis for transposition and determine their role(s). 2) To determine the functions of Ty-encoded gene products in transposition, with particular emphasis on the later (integration) step(s) of transposition. 3) To identify host functions required for Ty element transposition and determine their role. 4) To identify and characterize DNA intermediates in Ty element transposition. 5) To examine the factors influencing target specificity of Ty insertion.